The present invention relates generally to multi-carrier communication and, more particularly, to a method for mitigating impulse noise and interference in a multi-carrier communication system.
Market demand for high data rates plays an important role in advanced communications. With the development of “digital signal processor” (DSP) and “very large scale integrated circuit” (VLSI) technology, the demand for video/audio services, consumer services, Internet, and Word Wide Web (WWW) grows exponentially. An advanced communication technology is needed to satisfy the requirement. Moreover, it may be important to take advantage of existing communication infrastructure to transfer data so that servers and clients can save the cost for building a new network. “Asymmetric digital subscriber line” (ADSL) has become a popular application because ADSL technology satisfies the demand for more throughput based on a currently available infrastructure. For example, ADSL may share the same line as a telephone line by using higher frequencies than the voice band.
In the ADSL and next-generation xDSL systems, the adopted modulation approach is discrete multi-tone (DMT) technology, which is a multi-carrier modulation scheme that divides a channel into sub-channels. A DMT communication system may carry information from a transmitter to a receiver over a number of sub-carriers or tones. Due to channel dispersion or multi-path effect, interference or noise may corrupt the information signal on each tone as the signal travels through the communication channel (i.e., twisted pair telephone line) to the receiver. To ensure a reliable communication between transmitter and receiver, each tone may carry a limited number of data bits. The number of data bits that a tone can carry may vary from tone to tone and depend on the relative power of the information-carrying signal and the corrupting noise or interference on that particular tone.
In addition to additive white Gaussian noise (AWGN), near-end crosstalk (NEXT) and far-end crosstalk (FEXT), interference from alternating-current (AC) power lines is a significant source of impulsive noise on twisted pair phone lines. Furthermore, electric motors, light dimmer switches, hair dryers, malfunctioning light bulbs, lighting and the like are typical examples of environmental interference sources. The interference from impulse noise sources tends to be periodically impulsive, that is, relatively large in power level and short in duration. In the presence of such repetitive impulsive or burst noise sources, if their effects are not properly mitigated, system parameters may deviate from their nominal or optimum values. If the repetition rate of such impulsive noise is greater than the convergence rate of these system parameters' adaptation or estimation, deviations of the system parameters may accumulate and thus system performance may severely degrade.
Many mechanisms and approaches have been proposed to address the issue of impulse noise. Such mechanisms may focus on impulse noise detection, impulse noise management, or system parameter settings and adaptation based on monitored impulse noise characteristics so as to protect data and packets from impulse noise, assuming that receiver operations or signal reception mechanisms are not severely affected by impulse noise. In other words, the receiver's operations and timing are assumed to be not affected by impulse noise, either weak or strong. Such an assumption may not be true in real applications, especially in the presence of strong impulse noise or interference. The interference or impulse noise may severely degrade the quality of DSP and/or channel estimation for the setting of system parameters during the link setup stage, or significantly affect the adaptation or adjustment of system parameters in the showtime stage of data reception and transmission. It may therefore be desirable to have apparatuses and methods to prevent or reduce the impact of impulsive noise effects on system parameters and protect receiver operations in signal reception from corruption by impulse noise during link setup and showtime stages.